Effect of pore orientation on shear viscoelasticity of cellulose nanocrystal/collagen hydrogels

Motivated by a need to replicate structural and viscoelastic properties of soft tissue, such as cartilage, the structural hydrogels with viscoelastic feature have been of interest in biomedical application. However, the effect of pore alignment on their viscoelastic properties has been largely underestimated. This work prepared cellulose nanocrystal (CNC)/collagen hydrogels with different pore orientations, including horizontally aligned pores, random pores and vertically aligned pores, and integrated them into a multilayered hydrogel with multi-structure which mimics cartilage construct. The stress relaxation rate (tau(1/2)), creep rate (gamma(1/2)), storage modulus (G ') and loss modulus (G '') increased in the order of the vertical, random, multi-structural, and horizontal.G ' value of the horizontal increased up to 300% relative to the vertical in the strain amplitude and frequency sweep. Maxwell-Weichert and Variable Network Density models were used to explain phenomena, and the experimental curves fitted well with the theoretical models. These results reveal that the viscoelastic properties of hydrogel can be influenced by pore orientation except conventional component concentration.